Volatile Metabolite Profiles of Four Bacillus spp. during Soybean Fermentation
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Fermented soybean products are now gaining global attention for their nutritional and functional benefits. Industrial-scale production of these foods requires reliable starter cultures with consistent and predictable metabolic traits. Although strain-level variation in Bacillus spp. is known to influence fermentation outcomes, the contribution of species-level characteristics remains insufficiently explored. In this study, one strain each of Bacillus licheniformis, Bacillus sonorensis, Bacillus subtilis, and Bacillus velezensis was inoculated into sterilized soybeans, and volatile compounds were analyzed using GC-MS over a 30-day fermentation period. A total of 30 volatile compounds were detected, of which 29 were affected by the inoculated Bacillus strains. Among these, 17 compounds increased in all four inoculated samples, and the increase in 10 of them was strain-dependent. B. subtilis produced acetic acid, propanoic acid, and ethyl 2- phenylacetate exclusively, while butane-2,3-diol and 2-methylpropan-1-ol were specific to B. licheniformis, and octan-3-one was specific to B. sonorensis. These compounds contributed significantly to the distinct factor score directions in the principal component analysis. B. subtilis exhibited a volatile profile relatively similar to that of B. velezensis, while B. licheniformis was more similar to B. sonorensis. These patterns paralleled their respective amino acid production profiles observed in our previous studies, suggesting a species-dependent metabolic signature. These findings highlight the consistent and distinct metabolic outputs of each Bacillus species and support the use of species-level characteristics as early selection criteria in developing fermentation starter cultures. A combined species- and strain-level screening strategy may enhance the standardization and functional optimization of fermented soybean products.
Abstract
Fermented soybean products are now gaining global attention for their nutritional and functional benefits. Industrial-scale production of these foods requires reliable starter cultures with consistent and predictable metabolic traits. Although strain-level variation in Bacillus spp. is known to influence fermentation outcomes, the contribution of species-level characteristics remains insufficiently explored. In this study, one strain each of Bacillus licheniformis, Bacillus sonorensis, Bacillus subtilis, and Bacillus velezensis was inoculated into sterilized soybeans, and volatile compounds were analyzed using GC-MS over a 30-day fermentation period. A total of 30 volatile compounds were detected, of which 29 were affected by the inoculated Bacillus strains. Among these, 17 compounds increased in all four inoculated samples, and the increase in 10 of them was strain-dependent. B. subtilis produced acetic acid, propanoic acid, and ethyl 2- phenylacetate exclusively, while butane-2,3-diol and 2-methylpropan-1-ol were specific to B. licheniformis, and octan-3-one was specific to B. sonorensis. These compounds contributed significantly to the distinct factor score directions in the principal component analysis. B. subtilis exhibited a volatile profile relatively similar to that of B. velezensis, while B. licheniformis was more similar to B. sonorensis. These patterns paralleled their respective amino acid production profiles observed in our previous studies, suggesting a species-dependent metabolic signature. These findings highlight the consistent and distinct metabolic outputs of each Bacillus species and support the use of species-level characteristics as early selection criteria in developing fermentation starter cultures. A combined species- and strain-level screening strategy may enhance the standardization and functional optimization of fermented soybean products.